In a mobile communication system, a User Equipment (UE) can perform an inter-cell movement, and a system should determine an approximate location of the UE so as to perform a paging corresponding to the UE. If the UE is activated, since the UE performs a handover during the inter-cell movement of the UE, the system may determine the location of the UE. However, if the UE is in an idle mode, then the UE moves without a handover. Therefore, in this case, the UE performs a Location Area Update (LAU) or a Tracking Area Update (TAU) in order to register the location of the UE to the system. Accordingly, the system can perform the paging corresponding to the UE via Base Stations (BSs) belonging to a Location Area (LA) or Tracking Area (TA) to which the UE is registered.
However, if the paging is performed while the UE performs the LAU or TAU process, then a paging message may be transmitted in cells belonging to a previous LA or a previous TA. In this case, the paging message may be missed. That is, when an LA Identifier (LAI) or a TA Identifier (TAI) is changed due to a UE movement, and thus, the LAU or the TAU must be performed, then a paging transmission may start in a cell, to which the previous LAI/TAI belongs, during the LAU/TAU. As a result, there may be a case where the paging may not be delivered to a UE which moves to a cell to which a new LAI/TAI belongs. A situation of missing the paging message will be described below in greater detail.
When the LAI/TAI is changed and, thus the LAU/TAU is performed, then the paging transmission may start in a cell to which the previous LAI/TAI belongs during the LAU/TAU process. In preparation for this case, by using an inter-system paging or a roaming retry, a function of delivering the paging to an LAI/TAI to which a current cell belongs, after the completion of the LAU/TAU is implemented in a BS. However, due to several situations and/or features of the BS, such as a timer, etc., missing of the paging is frequently observed in practice in an LAI/TAI boundary area.
In addition, if the UE supports a multi-mode capable of providing accessing to different types of Radio Access Technologies (RATs), then the paging may be missed during an inter-network reselection process. For example, in case of moving between a 3rd Generation (3G) network and a 4th Generation (4G) network, if the paging starts to be delivered using a previous RAT, i.e., a 3G RAT, during an RAT change process, the paging proceeds through the 3G network. As a result, all subsequent paging may be missed, which leads to a reception failure in a case of voice telephony. More specifically, the paging that is missed during the RAT change process is illustrated in FIG. 1 and FIG. 2 to be described below.
FIG. 1 illustrates a signal exchange for an RAT change in a mobile communication system according to the related art.
Referring to FIG. 1, a UE 120 has a first communication module 121 and a second communication module 122. The first communication module 121 provides an interface for a first RAT, and the second communication module 122 provides an interface for a second RAT. For example, the first RAT may be a Long Term Evolution (LTE) network, and the second RAT may be a Universal Mobile Telecommunications System (UMTS). In order to move to the first RAT while the UE 120 is in a state of initially accessing the second RAT, the second communication module 122 transmits a measure request to the first communication module 121 in operation 101, and the first communication module 121 transmits a measure report including a measurement result to the first communication module 121 in operation 103. In operation 105, the second communication module 122 transmits a reselection request to the first communication module 121. The first communication module 121 transmits a reselection confirm in operation 107, and transmits a TAU request to a BS 110 in operation 109. In operation 111, a Base Station (BS) 110 of the first RAT performs the TAU process, and thereafter transmits a TAU accept. During the aforementioned process, a paging delivered through the second RAT may be missed between a time of delivering the reselection request in 105 and a time of delivering the TAU accept in operation 111.
FIG. 2 illustrates an example of paging missing during an RAT change process in a mobile communication system according to the related art.
Referring to FIG. 2, a signal exchange between a first communication module 221 and a second communication module 222, and a Paging Frame (PF) in a second RAT, are illustrated in FIG. 2. As illustrated in FIG. 2, after the occurrence of a PF P0, a measure report, or the like, is complete, and thereafter if a reselection condition is satisfied, a network reselection starts. In this case, the reselection starts if a related timer expires and if a candidate cell of the first RAT is included in a ranked list. Thereafter, the first communication module 221 transmits a TAU request to the first RAT, and receives a TAU accept/reject. From a start time of the reselection up to a reception time of the TAU accept/reject, only the first communication module 221 engages a Radio Frequency (RF) module in order to perform the TAU process, and, even if there are a plurality of RF modules, the second communication module 222 may be in an inactive state due to a decrease in a power consumption amount or the like. Therefore, in general, if a paging starts by using the second RAT, which is a previous RAT, during the TAU process, then a UE may not receive the paging after reselecting the first RAT. That is, a paging missing interval 230 occurs, and a paging message is missed in the second RAT through frames P1 and P2.
As described above, due to the LAU/TAU process after the UE movement or the RAT change, the paging message delivered through a previous cell or a previous RAT may be missed. Therefore, there is a need for a method for decreasing a probability of missing the paging message.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.